Pathway Simulation: Why?
Your emergency department is struggling.
You could try a range of different things…
- increase the number of staff available to register, triage or treat
- increase the number of rooms or beds
- increase the rate at which tests can be processed
- add a new step in the process with a different kind of practitioner
- completely redesign the pathway
Which of these is the right answer?
Queue, Queue, Barney McGrew
Healthcare tends to be full of queueing problems like this one.
- People attending a walk-in clinic or emergency department
- People calling a telephone-based service like 111 or a mental health crisis line
- People on a cancer diagnosis and treatment pathway
- People waiting to be assessed for ADHD and Autism, or on the waiting list for a gender clinic
- People waiting for a series of treatment with a mental health practitioner
- might have one, several or many appointments
Pathway Parts
Healthcare systems are full of resources
- People 👩🏻⚕️ 👩🏿⚕️ 👨🏽⚕️ 👨🏽⚕️ 👩🏾⚕️
- Equipment 🔬🩺
- Rooms & cubicles 🏥
- Beds 🛌🏻 🛌🏽 🛌🏿 🛌🏻 🛌🏼 🛌🏽 🛌🏿
- Treatments 💉 🩹 💊
- Vehicles 🚑 🚁 🚗
These resources experience demand from entities.
These entities might be
- People (in person) 🤒 🤢 🤧
- People (on the phone) ☎️
- Test Requests 🩻 🧪
Pathways and Queues
As these entities move through a pathway - a series of steps where these resources are used - queues can build up where there isn’t enough resource.
Queue What?
And these pathways are often very complicated!
There are lots of moving parts, and lots of variation.
Variation in when, and how frequently, people arrive
Variation in how long an activity in the pathway takes
Variation in the pathways people take within a single system
The Problem with Pathways
Making changes to pathways can be
And even if you do fix the original problem you were trying to solve, there’s a risk of knock-on effects elsewhere in the pathway that you didn’t foresee.
The Future Problems with Pathways
And even if you avoid that….
A system that is coping now might not cope
- all the time
- if demand increases
- if resource temporarily decreases
It’s All a Simulation
On HSMA, we teach a couple of different computer simulation techniques.
System Dynamics
High-level technique that’s often suited to uncovering fundamental issues with pathway or wider healthcare system design
Agent-Based Simulation (ABS)
Individual-level modelling that is particularly interested in the impact of individuals’ decisions and interactions
Discrete Event Simulation (DES)
Modelling focussing on the flow of entities through a pathway and use of resources, allowing detailed investigation of capacity, queues and waits
It’s Our DEStiny
What we generally want to tackle our pathway problems in healthcare is Discrete Event Simulation (DES)
DES to the Rescue
DES is so powerful because it gives us an in-silico (computer-based) reproduction of our pathway to play around with.
We can make any change we want
(e.g. more resources, higher demand, new pathway design)
safely and for free and see what impact it has on any metric we care to measure:
- how long people wait at each step of the pathway
- people meeting targets (e.g. 4 hour wait)
- how much of the time the resources are utilised for
And so on!
Variation
That randomness and variation in our healthcare systems that we mentioned before? DES can cope really well with that!
Let’s imagine that people turn up to our system, on average, every 10 minutes.
However, sometimes no-one turns up for half an hour, and other times 3 people turn up simultaneously.
By using distributions we can produce random times that mimic real-world patterns.
Randomness
Taking it even further, we can harness that variation for making the most of our models.
We can hold the random patterns consistent and change resource levels or pathway design
We can hold resources or pathway design consistent and allow randomness
This allows us to be sure the changes we’re testing really are responsible for the differences
This allows us to test our system in multiple parallel universes, running it tens or even hundreds of times!
A Note About Modelling
Your DES won’t be a perfect one-to-one reproduction of the pathway you are modelling.
We have to make certain assumptions and simplifications, and we can’t capture every complexity.
However…
All models are wrong, but some are useful
• George E. P. Box
DES is popular!
- On the HSMA programme, we’ve had over 35 projects using DES in some capacity
- A third of the registered projects this year use DES (as opposed to machine learning, ABS, system dynamics, natural language processing, geographical modelling)
- It’s also frequently used in the PenCHORD team
Example 1: Bladder Cancer Pathway
In this PenCHORD project, a DES model of the bladder cancer pathway at Royal Cornwall Hospitals Trust (RCHT) exposed two key system bottlenecks.
- A delay between patients being referred and receiving their surgery
- A delay waiting for the nurse specialist to contact the patient to discuss their diagnosis and treatment options
The model was used to support an on-the-spot rewrite of the pathway, resulting in multi-week reductions to waiting times.
Find Out More
Example 2: Vaccination Clinic
This HSMA project looked at the design of a COVID-19 vaccination clinic in North Devon, exploring
- queue lengths
- car park capacity
- times for each step of the vaccination process
The model identified potential issues with the original proposed plans, and was used to refine the plans to enable a safe but efficient delivery of the vaccination programme.
Find Out More
Example 3: Emergency Department Model
This HSMA project looked at ways to improve Urgent Treatment Care (UTC) performance. The team wanted to know
- What further staff and resources would be required for any variations in patient attendance
- How changes in the patient pathway would reduce bottlenecks
(e.g what would be the impact of front-loading diagnostics?)
The model identified a need for additional rooms and the ED was redesigned as a result.
Find Out More
Example 4: Mental Health Assessment Pathway Model
This PenCHORD project created a simulation model of a mental health assessment pathway.
The trust in question was piloting an approach that would allow patients to book their appointments themselves.
The model was used to help
- predict the number of appointment slots required at each site
- show that allowing queue-sharing between smaller groups of sites would significantly reduce the wait times
Find Out More
Example 5: Children’s Neurodiversity Assessment Pathway
This HSMA project created a model of a paediatric neurodevelopmental (ADHD + autism) pathway. Waits had increased to a 2 years on average.
The team wanted to understand
- where current bottlenecks in the process were
- what level of staffing would be needed to clear the existing backlog and maintain a steady state
The model showed that recruiting an extra lead clinician would not address the bottleneck - but an additional second assessor would.
Find Out More
Other Projects
You can find details about all of our previous and current Discrete Event Simulation projects on the HSMA website
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